A radiographic imaging device is a device that acquires images using radioactive isotopes and is one of the devices widely used in the nuclear medicine diagnostics and non-destructive inspection fields.
The radiographic imaging device used in nuclear medicine diagnostics, for example, a gamma camera using gamma rays or a SPECT device, provides functional information of the human body using a radiopharmaceutical unlike other diagnostic devices that provide structural information of the human body, such as magnetic resonance imaging (MRI) or ultrasound diagnostic devices.
FIG. 1 is a view showing a configuration of a conventional gamma camera 1. The general gamma camera 1 includes a collimator 10, and a radiation detector 20 configured to detect radiation passing through the collimator 10.
The collimator 10 functions as a sighting device for passing only gamma rays in a specific direction among the gamma rays emitted from the in vivo tracer and blocking gamma rays coming from other directions. In other words, the collimator 10 geometrically limits the gamma rays emitted from the living body region so that only the gamma rays emitted from the necessary sites are incident on the radiation detector 20.
The collimator 10 shown in FIGS. 1 and 2 shows an example of a multi-pinhole collimator (or a parallel-hole collimator) in which a plurality of holes are formed, and FIG. 3 is a view showing an example of a pinhole collimator having a predetermined acceptance angle θ.
Referring again to FIG. 1, the radiation detector 20 may include a scintillator 21, a light guide portion 22, and a photomultiplier tube 23. The gamma rays having passed through the collimator 10 are incident on the scintillator 21.
Herein, the gamma rays that have passed through the collimator 10 and reacted with the scintillator 21 are converted into low energy electromagnetic waves of a type that can be easily detected by the scintillator 21, and are amplified and converted into electrical signals in the photomultiplier tube 23 through the light guide portion 22, and the detected position or energy thereof is stored in a computer (not shown), thereby acquiring an image.
The above described SPECT device using the principle of gamma camera was firstly developed by W. I. Keys in 1976, and a device for brain SPECT was developed by R. J. Jaszczak in 1979.
The SPECT device, which is similar to the working principle of the gamma camera 1, is configured such that a single photon, for example, a radiopharmaceutical that emits gamma rays, is injected into the living body T, and transmission of the gamma rays generated in the living body is measured from various angles with a gamma camera installed in a gantry (not shown) rotating around the living body as shown in FIG. 2, and a tomographic image is acquired using an image reconstruction algorithm based on the detected signal.
Accordingly, as with the gamma camera 1, the collimator 10 and the gamma ray detector 20 are applied to the SPECT device.
FIG. 3 is a view illustrating the principle of a gamma ray imaging device 1a using a conventional pinhole collimator 10a applied to the gamma camera 1 or to the SPECT device.
Referring to FIG. 3, the pinhole collimator 10a is configured to have a predetermined acceptance angle θ and a predetermined hole diameter l. As a result, only the gamma rays incident within the range of the acceptance angle are formed to pass through the hole, and as described above, the gamma rays are selectively passed through by a geometry different from the multi-pinhole collimator 10.
The resolution and sensitivity of the gamma ray imaging device 1a using the pinhole collimator 10a are determined by the acceptance angle θ and the hole diameter l of the pinhole collimator 10a, a distance D1 between a subject and the pinhole collimator 10a, and a distance D2 between the pinhole collimator 10a and a gamma ray detector 20a. 
However, in the case of the conventional pinhole collimator 10a, since the acceptance angle θ and the hole diameter l are fixed, there is a problem that the resolution and the sensitivity are degraded according to the position and the size of the region of interest (ROI).
For example, it is possible to detect gamma rays emitted from a wider region as the acceptance angle becomes wider, but as shown in FIG. 3, since the ROI such as a lesion L is located in the living body T, when the pinhole collimator 10a having an acceptance angle capable of imaging the entire living body T is used, the resolution of the lesion L, which is the ROI, becomes low.
In particular, in the case of the SPECT device, imaging is performed while the device rotates around the living body, wherein in the case of using the pinhole collimator 10a with an acceptance angle θ fixed, since the position of the lesion is not fixed for each patient, the pinhole collimator 10a with an acceptance angle θ capable of imaging the entire living body is used.
In this case, as shown in FIG. 4a, the pinhole collimator 10a and the gamma ray detector 20a are rotated while being spaced apart from the living body by a predetermined distance to correspond to the acceptance angle, but the distance between the lesion L, as an actual ROI, and the pinhole collimator 10a changes, and in the case of an image acquired far from the lesion L, the resolution of the actual lesion L is inevitably lowered.
To solve this problem, recently, there has been proposed a method, in which the pinhole collimator 10a with the acceptance angle θ suitable for the location of the lesion L is replaced and then as shown in FIG. 4b, the distance from the lesion L, as an ROI, is measured to correspond to the acceptance angle θ.
However, the method shown in FIG. 4b is problematic in that since the distance between the lesion L, as an ROI, and the pinhole collimator 10a is increased and thus the sensitivity of the image is decreased, more radioactive material should be injected to a patient to increase the sensitivity.
Further, as shown in FIG. 5, recently, the necessity of pinhole collimator with various pinhole shapes has been proposed and actually applied to products. In addition to the circular pinhole shape as shown in FIGS. 5a and 5b, a pinhole collimator with a polygonal pinhole shape is used as shown in FIGS. 5c to 5e. Further, in forming the hole diameter, a predetermined space may be formed in the vertical direction (see FIG. 5a), a thin space may be formed in the vertical direction (see FIG. 5b), or the cone region may be realized as a polygonal shape and the diameter portion may be formed as a circular shape (see FIGS. 5c and a d). Alternatively, it may be made asymmetrical in the vertical direction (see FIG. 11).
When the various types of pinhole collimators as described above are applied to a radiographic imaging apparatus such as a conventional gamma camera, it is disadvantageous in that depending on the application field, a pinhole collimator of a required type should be purchased and replaced.
To solve this problem, recently, in the document of Korean Patent No. 10-1364339 filed by the applicant of the present invention, there has been disclosed ‘Variable pinhole type collimator and radiographic imaging device using the same’, in which an acceptance angle of the pinhole collimator is adjustable.
However, the above pinhole collimator is problematic in that since it is configured such that a plurality of apertures is laminated to adjust the acceptance angle or direction of the pinhole, a plurality of plates should be used to form one aperture, and as a result, the number of laminated plates is increased by the number of apertures constituting the pinhole collimator multiplied by the number of plates constituting one aperture, thereby increasing the thickness of the pinhole collimator.
Further, in the case of the area where the aperture narrows, especially the hole diameter part, For example, even if one aperture constitutes a hole diameter, the hole diameter is formed by overlapping a plurality of plates by a plurality of laminated plates constituting one aperture, thereby being restricted in the formation of pinhole with higher precision.
Further, a driving unit for adjusting each aperture is required for each aperture, which complicates driving and increases the entire size and weight of the collimator. When this is applied to the SPECT device, the weight of the gantry is increased, which is a constraint to implementation of the gantry rotation mechanism.